🌡️Heat Pump

ALERT 86

Lennox · XP21 Dave Lennox Signature Collection 20 SEER Heat Pump

Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump ALERT 86 Error Fix: Ignition Failure — Furnace

Furnace has failed to ignite after trial-for-ignition period. Equivalent to LED blink code 8 FLASHES. Same troubleshooting: check igniter, gas supply, flame sensor, gas valve.

High severity2 fixes available

Quick Answer

Error ALERT 86 on the Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump means: Ignition Failure — Furnace. The top-ranked community fix is “Test and Replace Igniter, Flame Sensor, or Gas Valve” (medium difficulty, ~60 min, DIY cost: $20-$50). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · heat pump

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many heat pump repairs can be done safely at home, consider hiring a qualified technician if:

This is a high severity error — continued use may cause damage or a safety hazard
The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $150-$300.

Other Lennox Models with Error ALERT 86

XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner

air_conditioner · 2 fixes

XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner

air_conditioner · 2 fixes

XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump

heat_pump · 2 fixes

Other Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump Error Codes

1 FLASH YELLOW

High Pressure Switch Open

2 fixes

2 FLASHES YELLOW

Low Pressure Switch Open

2 fixes

3 FLASHES YELLOW

Compressor Thermal Overload

2 fixes

4 FLASHES YELLOW

Short-Cycle Protection

2 fixes

ALERT 1

Communication Loss — Outdoor Unit

2 fixes

ALERT 11

High Pressure Protection — Outdoor Unit

2 fixes

ALERT 12

Low Pressure Protection — Outdoor Unit

2 fixes

ALERT 14

Compressor Discharge Temperature High

2 fixes

People Also Ask About Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump Error ALERT 86

What does error code ALERT 86 mean on a Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump?

Error code ALERT 86 on the Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump means: Ignition Failure — Furnace. Furnace has failed to ignite after trial-for-ignition period. Equivalent to LED blink code 8 FLASHES. Same troubleshooting: check igniter, gas supply, flame sensor, gas valve.

How do I fix error code ALERT 86 on my Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump?

The most successful fix is "Test and Replace Igniter, Flame Sensor, or Gas Valve" (medium difficulty, ~60 minutes). Estimated DIY cost: $20-$50. HomeMD has 2 community-ranked fixes for this error.

Is error code ALERT 86 on a Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump serious?

This error is rated high severity. You should address it promptly — continued use could cause damage or safety concerns.

Can I fix Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump error ALERT 86 myself?

Yes — the top-ranked community fix ("Test and Replace Igniter, Flame Sensor, or Gas Valve") is rated medium difficulty and takes about 60 minutes. Tools needed: Multimeter, Nut driver set, Phillips screwdriver.

How much does it cost to repair Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump error ALERT 86?

DIY cost: $20-$50. Professional repair typically costs $150-$300. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump have?

The Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump has 8 other known error codes, including: 1 FLASH YELLOW (High Pressure Switch Open), 2 FLASHES YELLOW (Low Pressure Switch Open), 3 FLASHES YELLOW (Compressor Thermal Overload), 4 FLASHES YELLOW (Short-Cycle Protection), ALERT 1 (Communication Loss — Outdoor Unit), and 3 more.

Which other Lennox models have the ALERT 86 error?

Error code ALERT 86 also appears on 3 other Lennox models: XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner, XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner, XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump have?

The Lennox XP21 Dave Lennox Signature Collection 20 SEER Heat Pump has 8 other known error codes:

1 FLASH YELLOW — High Pressure Switch Open (2 fixes)
2 FLASHES YELLOW — Low Pressure Switch Open (2 fixes)
3 FLASHES YELLOW — Compressor Thermal Overload (2 fixes)
4 FLASHES YELLOW — Short-Cycle Protection (2 fixes)
ALERT 1 — Communication Loss — Outdoor Unit (2 fixes)
ALERT 11 — High Pressure Protection — Outdoor Unit (2 fixes)
ALERT 12 — Low Pressure Protection — Outdoor Unit (2 fixes)
ALERT 14 — Compressor Discharge Temperature High (2 fixes)

Which other Lennox models have the ALERT 86 error?

Error code ALERT 86 also appears on 3 other Lennox models:

XC21 Dave Lennox Signature Collection 21 SEER Variable-Capacity Air Conditioner (air conditioner) · 2 fixes
XC25 Dave Lennox Signature Collection 26 SEER Variable-Capacity Air Conditioner (air conditioner) · 2 fixes
XP25 Dave Lennox Signature Collection Variable-Capacity Heat Pump (heat pump) · 2 fixes

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